Method for vacuum aeration of septic tanks to provide low pressure microbubbles

ABSTRACT

An improved method for aeration of septic tanks and the like by drawing atmospheric air into an expansion chamber and from there into agitated sludge to provide low pressure small microbubbles which have long hold times in the sludge material.

CROSS REFERENCED TO A RELATED APPLICATION

“This is a continuation of application Ser. No. 07/996,968 filed on Dec.23, 1992, now U.S. Pat. No. 5,951,867 which is a CIP of SN/969,001,filed Oct. 30, 1992, now abandoned.”

BACKGROUND OF THE INVENTION

This invention generally relates to a method for improved aeration forseptic tanks and the like.

Bacterial breakdown of sewage waste material is essentially performed byone of two basic processes, namely an aerobic process and an anaerobicprocess. The aerobic process requires oxygen for the bacteria to surviveand successfully decompose waste material. Emphasis upon the aerobicaction, as opposed to anaerobic bacterial action is preferred becauseaerobic bacteria decompose waste materials often without objectionableodors or the formation of objectionable gases. Aerobic bacteria need aconstant supply of oxygen on which to thrive, and therefore, suchaerobic systems require continuous replenishment of dissolved oxygenconsumed by the aerobes in the waste material. Additionally, agitationis necessary to prohibit waste particles from settling out to resistbacterial decomposition and form a continual buildup of sludge in septictanks and the like.

These requirements of aerobic systems have given rise to numerousmechanical aerators and agitators, including designs similar to thoseused in commercial sewage treatment plants. For example, devices havebeen designed to aerate the material by rotating paddle wheels or thelike which operate to either beat air into the material while moving itin the reservoir or to at least partially throw the material into theair. Other designs have incorporated separate means for moving thematerial in the reservoir and have introduced air by pumping compressedair through permeable “air stones” positioned at the bottom of thereservoir. The air stones are adapted to break the air into bubbleswhich enter the waste material. Bubbles are preferred over a stream ofair passing through the material because the ratio of surface area tovolume is greater and enables the oxygen to be more easily dissolved inthe material. The proper functioning of an aerobic system is, of course,dependent upon the quantity of dissolved oxygen that is present withinthe waste material. It is seen that more power would be consumed byinjecting larger than necessary quantities of oxygen into the materialand, therefore, economic considerations are important in the manner inwhich oxygen is introduced. Another important economic considerationinvolves the manner in which the material is moved around or circulatedwithin the reservoir.

Prior induced aeration systems most often insert air under pressure intothe waste mass which is being “broken up” simultaneously by agitation.As a result air becomes entrapped and bubbles form. However, because theair is under pressure and the liquid agitated, the bubbles formed arequite large. As a result they quickly rise to the surface and escape.This results in less than ideal sludge contact with the oxygen supply ofthe air. Thus, the amount of dissolved oxygen available for the aerobicbacteria is less then it might be if contact were prolonged.

A prior invention of one of the inventors (Blough), U.S. Pat. No.3,778,233, relates to an improved device for aeration used primarily inconfinement livestock operations to aerate sludge pits used inconjunction with such livestock operations. While that device works fineunder the circumstances of confinement feeding operations for livestock,such as hogs, there are limitations with use of such a device inconjunction with septic tanks that are used for storing human waste.

One of the problems with sewage disposal plants, and septic tank plantsare that often the disposal system finds itself “contaminated” withnon-organic non-biodegradable waste materials such as band-aids,sanitary napkins, disposable diapers, condoms, and other material thatpeople often discard into the lines of a sewage system. Theseadulterating materials can be drawn into the propeller of an aerationdevice such as that described in my previous U.S. Pat. No. 3,778,233. Asa result, the propeller often will become entangled in these materials,and the materials will plug the air tube lines. As a result, aeration isnot successfully achieved, and at best the sludge material is simplygenerally stirred or agitated by the propeller with little effect onbiodegradation. There is, therefore, a continuing need for an improvedaeration device of the general type disclosed in my previous U.S. Pat.No. 3,778,233, but of a design which is improved so that it can be usedsuccessfully for aeration in septic tanks that contain theabove-referred to “contaminating” non-organic, non-biodegradable wastematerials.

The development of such a device as now patented in Ser. No. 687,373,filed Apr. 18, 1991, now U.S. Pat. No. 5,194,144 would mean that septictanks can be conveniently converted into aeration units so that aerobicbacteria may decompose the material within the septic tanks, such thatit can be successfully used for uses such as yard fertilizer, etc.

A primary objective of the present invention is to provide an improvedaeration process of the type generally described in the above patent sothat it can be used for successful vacuum aeration of septic tanks toprovide low pressure microbubbles which are retained for longer holdtimes in a septic tank.

Another objective of the present invention is to provide an aerationmethod which provides ultra fine bubbles under equilibrium pressure withthe liquid media for aeration of septic material, so that they do notrapidly rise to the surface and exit the tank.

An even further objective of the present invention is to provide anaeration method which will keep the dissolved oxygen content in septictanks between 6 ppm and 10 ppm at all times to allow immediateconversation of all sizes of organic material particles by aerobicbacteria.

An even further objective of the present invention is to provide anaeration method which allows a home septic tank to be inexpensivelyconverted into an aeration unit for decomposition of human organic wastematerial.

The method and means of accomplishing these as well as other objectivesof the invention will become apparent from the detailed description ofthe invention which follows hereinafter.

SUMMARY OF THE INVENTION

An improved aeration method for septic tanks is provided. It may use anaeration device that has an elongated shaft having upper and lower ends.In operational position, the upper end of the elongated shaft ispositioned above the sewage level in the septic tank. Power means isassociated with the upper end for rotation of the shaft. The shaft has aconcentrically positioned air tube for drawing ambient air, as apposedto pressurized air from the upper end downwardly to the lower end. Thelower end has an associated propeller. The ambient air at atmosphericpressure is drawn down through an orifice and expands into a largerchamber or zone to the end of the air tube with air holes to allow freeescape of air bubbles into agitated waste material to aerate the same.The air since it is at atmospheric pressure does not expand as fast, andin fact due to the movement into a larger chamber is at reduced airpressure when the bubbles form. They are therefore smaller in size andhave an equilibrium pressure with the sludge resulting in the fine airbubbles, readily dispersed which have a long hold time to interact withthe aerobic organisms to enhance biodegradation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a septic tank in conjunction with afertilizer holding tank, with the septic tank being used with anaeration device for practice of the present invention.

FIG. 2 is a sectional view through a septic tank showing the directionalflow of materials when using the aeration method of the presentinvention.

FIG. 3 is an elevated view in partial section of an aeration device forpractice the present invention.

FIG. 4 is a sectional view along line 4—4 of FIG. 3 showing theconcentric relationship of the air tube, guard tube, and the bushingmounts for the associated motor for use in practicing the method.

FIG. 5 shows an end view along line 5—5 of FIG. 4, showing the detail ofthe propeller bushing and the mounting of the propeller on the rotatableshaft of an aeration device for practice of the method.

DETAILED DESCRIPTION OF THE INVENTION

Looking first at FIG. 1, it shows a conventional septic tank 10 fluidlyconnected via pipe 12 to associated fertilizer holding tank 14. Inaddition, septic tank 10 has a sewage inlet line 16. Sewage is fillingtank 10 up to the level represented by line 18. An aeration device forpractice of the present invention is represented in FIG. 1 at 20.

The details of the aeration device 20 for practice of the presentinvention are shown in FIGS. 3, 4 and 5. The device 20 can be used inconjunction with an electric timer 22 which is electrically connected tothe aeration device on/off switch 24 via electrical wires 26 and 28.Timer 22 has an electrically associated on/off light 30. In addition thedevice has an associated air filter 32 to allow ambient air to be drawninto the aeration device. The aeration device 20 is comprised of anelectric motor 34 having an output motor shaft 36 which is connected toan elongated shaft 38 such that shaft 38 will rotate with motor shaft36. Motor 34 is mounted in casing 40 via bushings 42. Bushings 42 holdsmotor 34 in a slightly elevated position on casing 40 to allow free airflow along the lines of directional arrows 44 and 46. At the lower endof shaft 38 is an axial thrust propeller 48. Thus, operation of themotor 34 rotates the shaft 38 and propeller 48 within the sludgematerial, moving it around the horizontal flow path indicated bydirectional arrows 50 of FIG. 2.

In addition to light 30, the unit may also have an audible indicator 31.This horn 31 is electrically connected to motor 34 to read the amperageof motor 34. A microprocessor (not depicted) records the startingamperage and the steady state amperage, after water is evacuated fromtube 52. Any change from the steady state condition is sensed and analarm from horn 31 is actuated to warn the operator that for some reasonthe unit needs to be checked. This assures that at all times duringoperation, successful aeration is occurring.

The same sensing of change in steady state operation may be accomplishedby other sensors. For example, one could use a light source, amechanical sensor such as a thermocouple, or a sensor source to sensethe water level in tube 52 for steady state conditions and to sense anychange away from steady state.

Concentrically positioned around shaft 38 is an elongated hollow airtube 52. Thus, when propeller 48 is rotating, atmospheric pressure airis drawn along the lines indicated by directional arrows 44 and 46 intothe space between shaft 38 and air tube 52 and flows downwardly asindicated by arrows 54 and 56. The air expands as it flows from thesmall space between shaft 38 and air tube 52 into the larger chamber asindicated at arrows 54 and 56. At the interface between rotatingpropeller 48 and the downwardly moving air 54 and 56, an extreme amountof agitation and disruption occurs such that the air is pulled throughair holes 60 in bushing 58 into the sewage material and septic tank 10in the form of extremely small air bubbles. Because the air is initiallyat atmospheric pressure and then expands, the bubbles are very small andnot pressurized. This provides the maximum amount of aeration since thesmaller the bubbles and the less air pressure the more the exposure ofsludge material to the oxygen since they are held longer in the sludge.Generally, with the device of this invention the dissolved oxygencontent in the septic tank can be kept between 6 ppm and 10 ppm at alltimes, which is sufficient to convert immediately all soluble organicmaterial into digested waste material suitable for transfer to hold tank14 and ultimate use as a fertilizer material which contains nitrates andphosphates and extremely fine particles of non-biodegradable solids.

As earlier indicated, forced air compressors insert air into water underpressure. This results in high pressure bubbles 4.2 mm diameter andlarger. These large bubbles rise rapidly to the water surface whichreduces lateral oxygen transfer efficiency due to the short entrainmenttime. The vacuum microbubble process, here practiced, reduces bubblesize, internal bubble gas pressure, increases surface to volume gaswater transfer area, and keeps the small bubble suspended for longerentrainment. As a result there is greater lateral oxygen transfer time.

Atmospheric air (250 cu ft per 24 hours with continuous run time) ispulled through a 2″ diameter plastic tube column and drawn through asmall orifice into an area of reduced pressure created by the withdrawnwater vacuum effect. The larger vacant area causes the air drawn throughthe orifice to expand due to the lower pressure according to the Gas LawV1P1=V2P2 at constant temperature. When this negative pressure air ispulled into the water vortex, the water collapses around the reducedpressure air and the surface tension generates a “microbubble” with anaverage size of 0.25 mm (range of less than 0.1 mm to 1 mm) beingdispersed throughout the medium. These dispersed condensed microbubblesremain suspended for prolonged time periods and slowly rise to thesurface over several hours of time (10-12 hours). This prolongedentrainment time due to equilibrium conditions allows increased lateraloxygen transfer to replace fluid dissolved oxygen (DO) used by aerobicbacterial digestion of organic matter (BOD, Biological Oxygen Demand).

Tests, performed on a 750 gallon septic tank which received 400 gallonsof 220 ppm BOD per day over a 118 day test run, using the device heredepicted to perform the method here described, reduced BOD values to anaverage of 56 ppm within the 24 hour testing period. One sample dumped400 gallons of 660 ppm BOD wastewater that was reduced to 70 ppm BODeffluent in the 24 hour period. This 90% reduction reflected a 24 hourconversion of 2.229 lbs of BOD to 0.236 lbs of BOD. At two pounds ofoxygen used per pound of BOD, 1.993 pounds of BOD used 3.986 pounds ofoxygen. The aerator pulled 4.12 pounds of oxygen in this time period andthe bacteria used 3.986 pounds of oxygen which represents a 96/7% oxygentransfer efficiency (OTE) from suspended gas bubbles to DO to metabolicactivity. Existing air compressor systems have an OTE of only 10% forvolumes pumped at 2500 cu ft per minute through a 24 hour time period.

This low pressure microbubble process generates millions of microbubbleswith a large surface to volume ratio for high OTE. With the optimumconditions of high oxygen, waste matter for food, and an aerobicbacterial population, metabolism and growth will proceed at anexponential rate maximizing waste matter oxidation. When waste matter islimited, bacteria consume the necessary oxygen and microbubbles areretained in reserve to handle fluctuating waste matter levels. Thisprocess maintains a natural DO saturation from air transfer.

Photographic evaluations of liquid entrained microbubbles used foraerobic wastewater digestion are based on the following: 0.25 mm averagebubble size, a measured population of 103 million microbubbles per cubicfoot of liquid, a combined air/water surface to volume of 283 squarefeet per cubic foot of liquid. The total microbubble volume wascalculated as 311 cubic feet per day with 0.0175 lbs of oxygen per cubicfoot of air at sea level. This produced (0.0175×311 cu ft) 5.44 lbs ofoxygen available for DO replacement per day. This compares to the oxygendemand satisfied for the 660 ppm BOD load digested to 70 ppm BOD in a 24hour period.

The microbubble process forms reduced air pressure small diameterbubbles that remain water suspended for prolonged time periods. Thispopulation of microbubbles provide replacement molecules for the DOassimilated by the aerobic bacteria during metabolic breakdown oforganic matter into carbon dioxide and water waste. No odor, lowsuspended solids, reduced BOD, and low coliform counts result.

Turning back to the construction of the aeration device for practice ofthe present invention, air tube 52 allows air to be pulled downwardlywhen propeller 48 turns. Air tube 52 extends downwardly slightly longerthan the terminus of propeller 48. In actual operation, bushing 58 withair holes 60, coacts with the end of air tube 52 to preventcontaminating foreign materials which are non-biodegradable plasticmaterials, synthetic rubber materials, etc. from interfering with thesmall bubble action of propeller 48. As illustrated in FIG. 5, propeller48 is mounted to the end of shaft 38 via propeller bushing 58. Propellerbushing 58 has air holes 60 to allow air to be forced into the sewagematerial.

In actual operation the unit is operated by timer 22 to run on an on/offcycle as recommended, depending upon the conditions in septic tank 10.Generally for household septic tanks on/off times of ten minutes on andtwenty minutes off are suitable operational periods. When the unit isenergized and electric motor 34 is operating, the unit operated in thefollowing manner. Motor 34 causes motor shaft 36 to rotate. Since motorshaft 36 is connectively coupled to shaft 38 it likewise rotates.Rotation of shaft 38 causes propeller 48 to rotate. Air or oxygen flowsthrough the gaps caused by bushings 42 via directional arrows 44 and 46down into the space of air tube 52, concentrically positioned aroundshaft 38. The air or oxygen flow moves downward to the backside ofpropeller 48. At propeller 48 the moving thrust of the downwardly movingair interfaces with the sludge material, and the high degree ofagitation results in a fine mist of air bubbles being dispersedthroughout sludge in septic tank 10. Material in septic tank 10generally moves along the lines indicated in directional arrows 50.

During operation the coaction of the location of the propeller withregard to the end of the air tube, and the action of bushing 58 incombination with air holes 60 coact to prevent adulterating orcontaminating material from being drawn into propeller 48 and fromplugging the air lines associated with air tube 52. As a result,non-organic waste adulterants such as non-digestible plastic or rubbermaterials that might be present in septic tank 10 do not interfere atall with operation of the unit which freely operated regardless of thesematerials to dispense micro-sized bubbles into the sludge and to freelycirculate and agitate the sludge material to maximize the operation ofaerobic bacteria.

It therefore can be seen that the invention accomplishes at least all ofits stated objectives. It goes without saying, certain modifications tothe construction and operation can be made and still employ the basicconcept and operational features of the invention. It is intended thatthose modifications be included within the claimed invention ashereinafter defined. For example other constructions of aeration devicesmay be used to pull in normal atmospheric air, reduce the pressure bypassing through an orifice into an expansion chamber and then draw theair into agitated sludge to interact with the aerobic organisms.

What is claimed is:
 1. A method of simultaneous aeration and agitationof hydrocarbon waste products, said method comprising; movingatmospheric pressure air through a confined zone into a larger zone ofreduced air pressure which contains hydrocarbon waste products;dispersing extremely small reduced pressure microbubbles of an averagesize of about 0.25 mm into the waste products while simultaneouslyagitating said waste products; and maintaining the dispersedmicrobubbles in said waste products to increase lateral oxygen transferto replace oxygen used by aerobic bacteria.
 2. The method of claim 1wherein the microbubbles are maintained within the waste products for upto ten to twelve hours.
 3. The method of claim 1 wherein themicrobubbles are produced by drawing atmospheric pressure air through anorifice into an expansion chamber and then into said waste products. 4.The method of claim 3 wherein said microbubbles are produced anddispersed by means of an air tube for drawing ambient air into apropeller agitation means rotating at high speed in said waste products.5. A method of simultaneous aeration and agitation of biological wastematerial, said method comprising; moving atmospheric pressure airthrough a confined zone into a larger zone of reduced air pressure whichcontains biological waste material; dispersing extremely small reducedpressure microbubbles of an average size of about 0.25 mm into the wastematerial while simultaneously agitating said waste material; andmaintaining the dispersed microbubbles in said waste material toincrease lateral oxygen transfer to replace oxygen used by aerobicbacteria.
 6. The method of claim 5 wherein the microbubbles aremaintained within the waste material for up to ten to twelve hours. 7.The method of claim 5 wherein the microbubbles are produced by drawingatmospheric pressure air through an orifice into an expansion chamberand then into said waste material.
 8. The method of claim 7 wherein saidmicrobubbles are produced and dispersed by means of an air tube fordrawing ambient air into a propeller agitation means rotating at highspeed in said waste material.
 9. A method of simultaneous aeration andagitation of biodegradable material, said method comprising; movingatmospheric pressure air through a confined zone into a larger zone ofreduced air pressure which contains biodegradable material; dispersingextremely small reduced pressure microbubbles of an average size ofabout 0.25 mm into the material while simultaneously agitating saidmaterial; and maintaining the dispersed microbubbles in said material toincrease lateral oxygen transfer to replace oxygen used by aerobicbacteria.
 10. The method of claim 9 wherein the microbubbles aremaintained within the material for up to ten to twelve hours.
 11. Themethod of claim 9 wherein the microbubbles are produced by drawingatmospheric pressure air through an orifice into an expansion chamberand then into said material.
 12. The method of claim 11 wherein saidmicrobubbles are produced and dispersed by means of an air tube fordrawing ambient air into a propeller agitation means rotating at highspeed in said material.
 13. A method of breaking down waste material byaerobic action, comprising: forming oxygen-containing bubbles having apressure less than atmospheric pressure; dispersing the bubbles into thewaste material such that the bubbles are suspended in the waste materialwithout rapid upward flotation, wherein the bubbles have an average sizeof about 0.25 mm; and agitating the waste material.
 14. The method ofclaim 13 wherein the bubbles are maintained in the waste material for atleast several hours.
 15. The method of claim 13 wherein the low pressureof the bubbles is produced by moving atmospheric air through an orificeinto an expansion chamber wherein the volume increases and the pressuredecreases.
 16. The method of claim 13 wherein the agitation is createdby a propeller rotating in the waste materials.
 17. The method of claim13 wherein the bubbles are air bubbles.
 18. A method of decomposingwaste material by aerobic action, comprising: dispersing extremely smallreduced pressure oxygen-containing microbubbles of an average size ofabout 0.25 mm into the waste products while simultaneously agitatingsaid waste products; and maintaining the dispersed microbubbles in saidwaste products to increase lateral oxygen transfer to replace oxygenused by aerobic bacteria.
 19. The method of claim 18 wherein themicrobubbles are formed from air.
 20. The method of claim 18 wherein themicrobubbles are maintained within the waste products for up to ten totwelve hours.
 21. The method of claim 18 wherein the microbubbles areproduced by drawing atmospheric pressure air through an orifice into anexpansion chamber and then into said waste products.
 22. The method ofclaim 18 wherein said microbubbles are produced and dispersed by meansof an air tube for drawing ambient air into a propeller agitation meansrotating at high speed in said waste products.